Typically, weather data, such as temperature or atmospheric pressure, is measured from a physical weather station or other physical weather parameter measuring device at a particular location. This weather data provided is generally collected, stored and made available to a user. The user upon collecting or receiving the weather data can further analyze, or make additional calculations using this weather data. For example, a user might take one or more weather parameters, such as temperature and calculate Evapotranspiration (ET), or amount of water used by a plant for those measured weather conditions. The user may then manually enter or communicate this value to an irrigation controller which in turn calculates the appropriate amount of irrigation based on the ET and the user input information.
FIG. 1 shows a prior art irrigation system in which a local weather station 112 located within an irrigation area 130 provides weather information that can be used to control an irrigation system 140 within the irrigation (site) area 130. The weather information can be stored in non-local storage 114, but still represents the weather at the site of the irrigation system. The irrigation system can also receive weather parameters from a non-local data source 116 (such as a satellite), but the data (weather information) of the non-local data source 116 reflects weather of the site (irrigation) area 130. A processor 150 receives the irrigation area weather information and controls the irrigation system 140.
Irrigation systems that include the above-described controller to control the amount of irrigation based on calculated ET can be sub-optimal because the physical weather measuring parameter device may be located somewhere other than where the irrigation area is located. Therefore, the calculated ET may not provide an accurate estimate of the irrigation required because the ET is calculated based on physical weather measurements that do not accurately represent the weather at the irrigation area.
Additionally, ET is generally calculated using grid based processing. With grid based processing, a value for a weather parameter to be used in the calculation of the ET is estimated using an average of the weather parameter within a specified cell of a grid. A disadvantage of grid based processing is that a weather parameter in the grid cell may have large variation within the grid. Typically, the weather parameter is averaged across the cell of the grid. This can result in a loss in accuracy depending on the weather parameter, the adjacent or associated weather parameters, and grid cell size.
It is desirable to accurately calculate an ET value for an irrigation area, when data for calculating the ET in the irrigation area is not available.